single-click for open recent documents in new Start Center

Change-Id: I34c6a5f9057707cdd1e2f4f82024818e7c8a6630
Signed-off-by: Rodolfo Ribeiro Gomes <rodolforg@gmail.com>
Reviewed-on: https://gerrit.libreoffice.org/6610
Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>